The present invention relates to data recorders and, more particularly, to digital data recorders adapted for remote access over dial-up telephone lines.
Since the earliest days of utilities providing energy in the form of gas and electricity, the consumption of energy has been metered at the user's location. Collecting the metered data has been done traditionally by a meter reader visiting the user's location at regular intervals to note the indication on an indicator such as, for example, dials or drums on an electro-mechanical register or an electronic display or digital readout. In one series of electric meters produced by the General Electric Company, readout accuracy and speed are enhanced by an optical readout device accessing the data through an optical port provided under the trademark Optocom.
Physical reading of registers in electric meters is a substantial burden on the utility providing the electric energy. It is thus desirable to provide means for the utility to read the consumption and time-dependent time-of-use and/or demand data from user's registers without requiring a personal visit by a meter reader.
One way to provide remote reading of a register includes a dedicated line such as, for example, a dedicated telephone line between a metering data center and a register in a consumer's facility. The metering data center is thereby enabled to query the condition of registers in the consumer's facility at will. From a practical standpoint, an energy consumer, absent a metering failure, requires a readout only at intervals of, for example, once a week or once a month. It is unlikely that a utility is cost justified in interrogating the registers of even a large energy consumer more frequently than once a day. Thus, the relatively high cost of a dedicated telephone line is difficult to justify, even in the case of a large energy consumer.
Another alternative includes the use of a dial-up telephone line with an auto-dial, auto-answer MODEM (modulator, demodulator) at the user's location. The amount of data that must be transmitted at any time between a metering data center and an energy user fits well with the data transmission rates of which commercial MODEM devices are capable.
It is preferred that a data-communications system used with the present invention be able to share telephone facilities with other uses such as, for example, normal incoming or outgoing voice communication. Such sharing requires that the system be able to recognize that the telephone line is in use, and to delay demanding use of the telephone line until it is free. It is further desirable that means be provided to permit the data-communications system to be accessed by an incoming call. Such means may include, for example, an auto-answer function in which the system engages the incoming line after a predetermined number of rings have elapsed.
Best advantage can be taken of access through a dial-up telephone line if the line can be used for other purposes when not needed by the data communications system. For example, the data communications system may be connected in parallel with the user's existing telephone line. Except for a few relatively short periods when the data communications system is in the process of communicating data with the metering data center, the user's line is undisturbed by the presence of the data communications system. Steps must be taken to prevent the data communications system from interfering with other uses and to prevent other uses from corrupting the transmitted data.